1. Field of the Invention
This invention relates to a speed reducer which can obtain a high speed reduction ratio by a single stage.
2. Related Background Art
Various speed reducing mechanisms have heretofore been proposed to make high speed rotation into low speed rotation, and speed reducers as shown below are known.
(1) First Example of the Conventional Art
A transmission using a plurality of stages of gear trains such as spur gears, bevel gears and worm gears or using planetary gears to effect speed reduction.
(2) Second Example of the Conventional Art
A transmission using a harmonic drive mechanism which is one type of mechanism utilizing a difference in the number of teeth to effect speed reduction.
(3) Third Example of the Conventional Art
A transmission using a resiliently deformable wave gear described in Japanese Laid-Open Patent Application No. 63-214544 which is another one of the mechanisms utilizing a difference in the number of teeth to effect speed reduction.
(4) Fourth Example of the Conventional Art
A transmission using a universal joint or a ball described in Japanese Laid-Open Patent Application No. 4-191546 and Japanese Laid-Open Patent Application No. 5-99283 to pivotally move a pivotally movable bevel gear, is another one of the mechanisms utilizing a difference in the number of teeth to effect speed reduction.
The transmission according to the above-described third example of the conventional art is shown in FIG. 5 of the accompanying drawings. In FIG. 5, the reference numeral 30 designates a wave gear having a toothed portion 30A formed on the peripheral portion of the end surface thereof. The reference numeral 31 denotes a speed change gear having a toothed portion 31A formed on the peripheral portion of the end surface thereof, the toothed portion 31A differing in the number of teeth from the toothed portion 30A. The reference numeral 32 designates the rotary shaft of a motor which forms an input shaft, the reference numeral 33 denotes an arm, the reference numeral 34 designates a roller provided on the tip end portion of the arm 33, and the reference numeral 35 denotes a chassis. In this transmission, the wave gear 30 urged by the roller 34 is resiliently deformed and the toothed portion 30A thereof is in meshing engagement with the toothed portion 31A of the speed change gear 31, and when the arm 33 is rotated about the rotary shaft, the meshing position shifts sequentially.
Assuming here that the wave gear 30 is fixed in the direction of rotation thereof, the speed change gear 31 is squeezed by one pitch each of the gear and is rotated. Accordingly, if for example, the number of teeth of the wave gear 30 is 64 and the number of teeth of the speed change gear 31 is 66, when the arm 33 effects one full rotation, the speed change gear 31 is rotated by an amount corresponding to the difference in the number of teeth because the difference in the number of teeth is two. That is, it is rotated by 1/33 (2/66).
The transmission according to the above-described fourth example of the conventional art is shown in FIG. 6 of the accompanying drawings. In FIG. 6, the reference numeral 40 designates a casing, the reference numeral 41 denotes an input shaft, the reference numeral 42 designates an input rotor, the reference numeral 43 denotes an input side gear, the reference numeral 44 designates a rotary bearing ball, the reference numeral 45 denotes an output shaft, the reference numeral 46 designates a detent roller pin, the reference numeral 47 denotes a slit groove, and the reference numeral 48 designates an output side gear. When the input shaft 41 is rotated, the input rotor 42 fixed to the input shaft 41 and formed with an inclined end surface is also rotated, and the input side gear 43 which is sliding contact therewith is pivotally moved about the rotary bearing ball 44.
The input side gear 43 is not rotated because the detent roller pin 46 mounted on the outer periphery thereof fits in the slit groove 47 formed in the casing 40. When the input rotor 42 which is in sliding contact with the back of the input side gear 43 effects one full rotation, the input side gear 43 is pivotally moved and the output side gear 48 partly meshing with the input side gear 43 is rotated by an amount corresponding to the difference in the number of teeth therebetween.
If for example, the number of teeth of the input side gear 43 is 100 and the number of teeth of the output side gear 48 is 99, when the input side gear 43 effects one full rotation, the input side gear 43 meshes with the output side gear 48 by an excess amount corresponding to the difference in the number of teeth because the difference thereof in the number of teeth from the output side gear 48 is one tooth. That is, it is rotated by 1/100.
However, the following problems are pointed out in the above-described examples of the conventional art.
(1) Regarding the First Example of the Conventional Art
When spur gears, bevel gears or planetary gears are used, 1/2 to 1/3 is suitable as a speed reduction ratio per stage of gears, and when an attempt is made to obtain a high speed reduction, a plurality of stages of gear trains become necessary, and this leads to the fault that the apparatus becomes bulky.
Also, when worm gears are used, a high speed reduction is obtained by a single stage, but generally transmission efficiency is as bad as 40%.
(2) Regarding the Second Example of the Conventional Art
The transmission using a harmonic drive mechanism can obtain a high speed reduction ratio by a single stage, but it is difficult to make the thickness small, and the number of parts is increased as by the use of ball bearings, and this leads to the disadvantage of expensiveness.
(3) Regarding the Third Example of the Conventional Art
This example is characterized by a resiliently deformable wave gear, and a resilient material is used for the gears and constantly deformed gears opposed to each other are forced to mesh with each other for use and therefore, from the viewpoints of the mechanical strength of the resilient member and the constitution of the constituent parts, this example is applied, for example, to compact products for public welfare which are low in torque and do not much require the accuracy of rotation and durability.
(4) Regarding the Fourth Example of the Conventional Art
Use is made of a pivotally movable gear and an output bevel gear formed of a rigid material, and the pivotally movable gear is regulated in the direction of rotation by the use of a universal joint or a pivot bearing using balls and a pin, and the shaft of the output bevel gear opposed thereto provides an output shaft, but from the viewpoint of the rigidity of the material forming the pivotally movable gear and output bevel gear, particularly the mechanism which can withstand even a high load from the output shaft side, and the constitution of the constituent parts, this construction is directed, for example, to products for industry and for heavy machines which are high in torque and moreover require durability.
Consequently, when this Example is used as a compact transmission, it becomes difficult for it to become compact, and particularly thin, and since a roller pin is used for the regulation of rotation, the roller pin strikes against a slit groove in a casing during rotation while being pivotally moved and thus, backlash is liable to occur, and this leads to the occurrence of backlash and the irregularity of rotation at the start.